BEIJING (REUTERS).- Four associates of Chinese artist-activist Ai Weiwei detained along with him in a controversial case were freed after Ai's release, friends of the artist said on Saturday.

The four included journalist Wen Tao, detained along with Ai in early April when the two were at Beijing airport heading to Hong Kong, said Liu Yanping, a volunteer worker involved in Ai's campaigning on rights issues.

"All of the people connected to the case have been released," Liu told Reuters by telephone.

"That's a big relief. But I do think the Ai Weiwei studio's work will remain suspended for now," she said, adding that she was referring to Ai's politically-charged activism, not to his artistic work.

The detention of Ai and his associates marked the start of the contentious case which the Chinese government said was about suspected tax evasion, while Ai's family and supporters said it was part of a political drive to silence him and other critics of the ruling Communist Party's censorship and controls.

Ai's accountant Hu Mingfen, a designer in Ai's studio, Liu Zhenggang, and the artist's driver, Zhang Jinsong, who all went missing in April, were also freed on Thursday or Friday, according to Liu, the volunteer, as well as Liu Xiaoyan, a lawyer close to Ai Weiwei.

The 54-year-old artist Ai (whose name is pronounced "Eye Way-way") was freed on bail on Wednesday, a day before Chinese Premier Wen Jiabao left for Europe, where he will visit Britain and Germany, two nations that decried Ai's detention.

The release of Ai and other activists has marked a stepdown of sorts by Chinese authorities, who have rarely flinched in prosecuting critics of Party rule.

But the tax charges and release conditions that hover over Ai and his released friends are likely to ensure they stay publicly silent for now.

Other Chinese dissidents and human rights lawyers detained and then released in recent months have also said they must stay quiet in return for their release.

Zhang, the driver, was also released on bail, said Liu Xiaoyan, the lawyer. But he and Liu Yanping, the volunteer, were unsure whether bail terms applied to the other three freed.

"My understanding is that Wen Tao is not allowed to speak out about what happened," said Liu Yanping. "I think the others will be in the same situation."

Officials have told Ai that he cannot speak out, tweet or travel without their permission for a year, a source close to the family told Reuters on Friday.

China has denied that the international outcry over the detention of Ai pressured Beijing into releasing him.

Analysts say Ai's release is far from a sign of a U-turn by the ruling Communist Party. Authorities have muzzled dissent with the secretive detentions of more than 130 lawyers and activists since February, amid fears that anti-authoritarian uprisings across the Arab world could trigger unrest.

(Reporting by Chris Buckley; Editing by Sugita Katyal)